Plating of electrical conductors on mechanically functional three-dimensional plastic parts is gaining increased acceptance in the mechanical and electrical design communities. These electrical/mechanical hybrid devices are generally known as "molded interconnect devices", or MIDs. There are a number of methods known for the manufacture of MIDs including electroplating, electroless plating, foil embossing, and circuit film in-molding. However, one of the limitation in each of these technologies is that they are not capable of plating more than a single electrical layer on each plastic surface. This is a severe limitation since most circuits designed today take advantage of multiple electrical conductor layers (for example, multi-layer FR-4 circuits).
Manufacturing methods such as gas assist injection molding, blow-molding and lost-core molding produce complex three-dimensional plastic or composite parts having internal cavities void of plastic material. These cavities generally serve the purposes of providing required structural support, reducing overall material usage in a part, and preventing poor molding features such as "sinks" or short shots.